Based on my armchair engineering skills, yes, I would also think that it adds a bit of progressiveness to the shock ratio as it goes through the stroke, i.s. making it harder to compress the shock the deeper into the travel you go. Also, it doesn't just serve to prevent shock twist, the upper link actually determines the position of the shock - without it, the shock would simply flip forward until it was aligned with the foremost pivot point of the swingarm (i.e. where the swingarm attaches to the shock).

Well for one thing, the system seems to allow them to run a very long shock, so the leverage ratio is going to be quite low. On a single pivot, we know that makes for good riding bikes (Makulu anyone) - chances are they didn't make this just to claim the title for the world's ugliest and most complex linkage system ever...